Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
181–188 of 188 · Normal
Question 181
8 marks · Normal
Answer and see the solution →The reaction between magnesium and dilute hydrochloric acid is used to investigate both the energy changes and the rate of the reaction.
(a)[1 mark]Write a balanced chemical equation for the reaction between magnesium and dilute hydrochloric acid.
(b)[2 marks]State whether this reaction is exothermic or endothermic. Explain your answer in terms of temperature change observed.
(c)[3 marks]Describe a simple experiment you could carry out to compare the rate of this reaction using magnesium powder and magnesium ribbon. Include the measurement you would take.
(d)[2 marks]Based on your knowledge of energetics and rates, explain why the reaction may occur faster with magnesium powder than with magnesium ribbon, but the temperature rise observed may be similar in both cases if the same mass is used.
Question 182
8 marks · Normal
Answer and see the solution →The reaction below is carried out in a laboratory and studied for both its energy profile and the effect of temperature on its rate:
(a)[3 marks]Draw a labelled energy profile diagram for this reaction given that the enthalpy change, , is negative.
(b)[2 marks]Describe what is meant by activation energy and indicate it on your diagram.
(c)[3 marks]The experiment is repeated at a higher temperature. Explain using collision theory how this affects the rate of the reaction.
Question 183
8 marks · Normal
Answer and see the solution →A student investigates the thermal decomposition of calcium carbonate and the effect of acid concentration on the rate of this process.
(a)[2 marks]Thermal decomposition of calcium carbonate is carried out: During an experiment, 2.50 g of calcium carbonate is heated, causing a temperature decrease in the surroundings from 25.0 °C to 18.1 °C. Assume all absorbed energy came from a nearby 150 g beaker of water (specific heat capacity ). Calculate the heat absorbed (Q) by the reaction mixture.
(b)[3 marks]Calculate the molar enthalpy change (ΔH) for the decomposition of calcium carbonate, in kJ/mol. (M_r of )
(c)[3 marks]In a separate rate experiment, the same mass of calcium carbonate is added to 50 cm³ of hydrochloric acid at two different concentrations (1.0 mol/dm³ and 0.5 mol/dm³). Predict and explain the effect of decreasing the concentration of the acid on the rate of CO₂ production.
Question 184
8 marks · Normal
Answer and see the solution →In an experiment, the enthalpy change of neutralisation between sodium hydroxide and hydrochloric acid is determined using calorimetry. The rate of the reaction is also studied using different concentrations of hydrochloric acid.
(a)[3 marks]Describe, in outline, how you would carry out a calorimetry experiment to measure the heat change for the neutralisation reaction.
(b)[5 marks]A student carries out the experiment twice: first with 1.00 mol/dm³ HCl and then with 0.50 mol/dm³ HCl, using the same volume and concentration of NaOH each time. State and explain the effect (if any) changing the concentration of HCl has on (i) the total heat evolved and (ii) the rate of temperature rise during the experiment.
Question 185
8 marks · Normal
Answer and see the solution →A student investigates the displacement reaction between zinc powder and copper(II) sulfate solution. She uses calorimetry and also measures how fast the blue colour disappears when she changes the reactant concentrations.
(a)[3 marks]Describe how you would carry out a calorimetry experiment to determine the enthalpy change for the reaction between zinc and copper(II) sulfate solution. Include the apparatus needed and key steps in your answer.
(b)In one experiment, the student adds 1.20 g of zinc to 50 cm³ of 0.200 mol/dm³ copper(II) sulfate solution in a polystyrene cup at 18.0°C. The maximum temperature reached is 27.5°C.
(i)[2 marks]Calculate the final concentration of copper(II) sulfate after the reaction, assuming all of it is used up. Give your answer in mol/dm³.
(ii)[1 mark]State one way the rate of this reaction can be measured during the experiment.
(c)The student repeats the experiment with 25 cm³ of 0.200 mol/dm³ copper(II) sulfate and 25 cm³ of distilled water (total volume still 50 cm³), keeping the amount of zinc the same.
(i)[1 mark]Calculate the new concentration of copper(II) sulfate before mixing with zinc.
(ii)[1 mark]Predict and explain how the lower concentration affects the rate of reaction. Use collision theory in your answer.
Question 186
8 marks · Normal
Answer and see the solution →A student investigates the temperature change when dilute hydrochloric acid reacts with excess solid magnesium carbonate. She collects the following data:
Data from neutralisation experiment Volume of HCl added (cm³) Initial temperature (°C) Maximum temperature (°C) 25.0 21.0 27.0 Separately, she wants to know how fast the reaction is at the beginning.
(a)[2 marks]Use the formula Q = mcΔT to calculate the heat evolved, Q, in joules during this experiment. Assume the final solution volume is 25.0 cm³, density is 1.0 g/cm³, and c = 4.18 J/g°C.
(b)[2 marks]Calculate the average rate of reaction in °C per minute if the temperature rose from 21.0°C to 27.0°C in 2.5 minutes.
(c)[2 marks]If a second experiment is done with half the concentration of hydrochloric acid, predict and explain (using collision theory) how the rate of temperature rise will change, assuming all other conditions are identical.
(d)[2 marks]State one source of error in this type of calorimetry experiment and suggest a way to minimise it.
Question 187
8 marks · Normal
Answer and see the solution →The following graph shows the rate of a reaction (in g/s) for different concentrations of hydrochloric acid, and gives data for a calorimetry experiment involving the neutralisation of hydrochloric acid with sodium hydroxide.
(a)Rates of reaction at different concentrations Concentration of HCl (mol/dm³) Rate (g/s) 0.20 0.013 0.40 0.026 0.60 0.039 0.80 0.052 (i)[1 mark]Describe the relationship between concentration and rate as shown in the table.
(ii)[1 mark]Explain this relationship using particle (collision) theory.
(b)A student mixes 25.0 cm³ of 1.00 mol/dm³ HCl with 25.0 cm³ of 1.00 mol/dm³ NaOH in a polystyrene cup. Initial temperature is 21.0°C and maximum temperature is 29.5°C. (i) Calculate the total volume of solution and the number of moles of HCl used. (ii) Calculate the heat evolved (Q) in joules. Assume density is 1.00 g/cm³ and c = 4.18 J/g°C. (iii) Calculate the molar enthalpy change (ΔH) for the reaction in kJ/mol.
(i)[1 mark]Calculate the total volume of solution and the number of moles of HCl used.
(ii)[2 marks]Calculate Q, the heat evolved, in joules.
(iii)[3 marks]Calculate the molar enthalpy change (ΔH) for the reaction in kJ/mol. Give your answer to 2 significant figures and state if the reaction is exothermic or endothermic.
Question 188
8 marks · Normal
Answer and see the solution →A student investigates the combustion of ethanol in air, measuring temperature rise to calculate enthalpy change and evaluating the reliability of results. She also experiments with the rate of a reaction between magnesium and hydrochloric acid under changed pressure.
(a)In a combustion experiment, 0.90 g of ethanol (C₂H₅OH, Mᵣ = 46.0) is burned to heat 120.0 g water. The temperature of the water rises from 20.0°C to 47.0°C. Assume c = 4.18 J/g°C.
(i)[2 marks]Calculate the heat absorbed by the water in joules.
(ii)[1 mark]Calculate the number of moles of ethanol burned.
(iii)[2 marks]Calculate the experimental molar enthalpy change (ΔH), in kJ/mol, for ethanol combustion. Use the correct sign and 2 significant figures.
(b)[2 marks]Suggest two sources of error in the calorimetry method that could explain why the experimental ΔH is less negative than expected.
(c)[1 mark]The student repeats a reaction between magnesium and hydrochloric acid, but increases the pressure (with all chemicals in solution). Describe and explain what effect, if any, changing the pressure will have on the rate of this reaction.